body {
    margin-top: 20vh;
    font-family: 'Inknut Antiqua', Roboto, serif;
    font-size: 1em;
    font-weight: normal;
}
.screen {
    height: 120px;
}
.result {
    font-size: 2em;
    margin-top: 10em;
}
.btn{
    float: left;
    height: 80px;
    font-size: 1.2em;
    border: 1px solid;
    width: 5.4vw;
    margin-left: -0.6vw;
}
.btn-special {
    width: 10.7vw;
}

/*置底页脚*/
body {
    display: flex;
    min-height: 80vh;
    flex-direction: column;
}

main {
    flex: 1 0 auto;
}

@media (max-width: 600px){
    body {
        margin-top: 2vh;
    }
    .btn {
        width:21vw;
        margin-left: -2vw;
    }
    .btn-special {
        width: 43.5vw;
    }
}